1. Field of the Invention
The present invention relates generally to agricultural vehicles. More specifically, the present invention relates to agricultural vehicles for distributing materials in fields having uneven terrain, which are capable of traversing formations such as levees, wash-outs, and the like.
2. Description of the Relevant Art
It is a common practice to spray agricultural fields using aircraft, especially those fields having uneven terrain. For example, most chemical application on rice is carried out by aircraft. However, this practice suffers from a number of drawbacks. The aerial spraying technique tends to be expensive and suffers from target spray drift, which tends to be a major source of environmental problems. Further, timely aerial application can be a problem because crop dusting aircraft cannot operate in high winds. Additionally, it is difficult to spray irregularly shaped fields using aircraft.
Conventional ground application spray rigs encounter difficulties in crossing rice levees, wash-outs, and other surface irregularities, especially conventional tractors, trucks, trailer sprayers, and self-propelled sprayers that use high pressure tires. These tires exhibit little or no flexure and apply a high force per unit area to the surface under the tire. This tends to crush and flatten freshly pulled or plowed levees and necessitates manual repair, using a hand shovel or the like, of the ruts created by the tires.
In addition to the damage to levees, conventional spray equipment has also suffered from a relatively large amount of mechanical breakage. This breakage is due largely to the vertically oriented jolting caused when a levee, wash-out, or other surface irregularity is traversed by the vehicle.
In an effort to overcome the above mentioned problems encountered with aircraft and conventional ground application equipment, and to ensure that timely spraying of agricultural crops and the like could be assuredly carried out irrespective of the ground and wind conditions, the applicant developed an ATV (all terrain vehicle) sprayer which exhibits excellent floatation capability on extremely soft ground.
This arrangement, as shown in FIG. 1, comprised an ATV prime mover and an ATV sprayer vehicle (trailer). Both the ATV prime mover and the trailer used very soft, low pressure elastic tires that exhibit very high flexing and floatation capabilities. The low weight of the ATV prime mover and ATV sprayer vehicle (hereinafter ATV sprayer) produced a low ground pressure and enabled the ATV prime mover and ATV sprayer to roll over soft ground without leaving ruts. This arrangement worked well on level land in corn, wheat and soybeans.
However, the ATV sprayer vehicle in this instance used a conventional tandem axle including a cross-beam bracing arrangement interconnecting the front and back axles and was arranged so that the front and rear axles were spaced equally on either side of the pivot or fulcrum point of the two axles. In other words, the front and rear axles were spaced in a fixed 1:1 relationship with respect to the point intermediate the two axles about which the vehicle tends to tilt.
Several features of this design prevented the ATV sprayer from crossing levees. The first was that the 1:1 axle spacing did not allow the vehicle to readily ascend the uphill face of a levee. Moreover, once on top of the levee, the vehicle chassis tended to straddle the levee and bring about the situation wherein the cross-beams that interconnect the front and rear axles either cut into or dragged across the top of the levee. The damage that resulted from this cutting or dragging action often was so severe as to require someone to use a shovel to manually repair the levee.
Another acute problem that was encountered is illustrated in FIG. 1. As shown in FIG. 1, after the prime mover 10, in this case a four wheel ATV, has crossed the levee or undulation 12, the rigid connection 14 between the ATV (prime mover) and the trailer (ATV sprayer) 16 tended to hold the trailer level, thereby preventing the trailer from assuming a posture conducive to uphill travel. Therefore, the leading wheels 20 were subjected to a force that tended to pull them "straight through" the levee 12 resulting in the generation of a moment of force that was sufficient to lift the rear wheels 22 off the ground in the manner illustrated in FIG. 1, and causing the ATV sprayer 16 to teeter forward.
This collision-like encounter with the front or ascending wall 12a of the levee produced an impact that was undesirably imparted to the spraying apparatus 24 mounted on the trailer 16 (ATV sprayer) and generated sufficient resistance, as the front wheels 20 tended to sink into the relatively soft wall 12a, to keep the ATV sprayer 16 teetering and, in some cases, to cause the ATV prime mover 10 to lose traction.
In addition to the conventional towed agricultural vehicles described above, self-propelled spray vehicles have also been used to apply agricultural materials to fields. These self-propelled vehicles typically have a high clearance chassis to permit application of chemicals, fertilizer, and the like to standing crops. One form of self-propelled vehicle 30 (FIG. 2) is supported by four wheels 31, 32 located at respective corners of the vehicle 30. The wheels 31, 32 are typically each driven by an individual drive mechanism (not shown) so as to provide a four-wheel drive for increasing traction in wet and uneven field conditions. Various types of suspension arrangements are associated with each of the wheels 31, 32 to help absorb jolts and stresses caused by levees, wash-outs, and so forth.
As shown in FIG. 2, the conventional self-propelled vehicle 30 has a significant drawback when operated in uneven terrain as a result of the single-wheel assemblies. For example, when the vehicle traverses a wash-out or ditch 33, as shown in FIG. 2, the front wheels 31 tend to drop suddenly to the bottom of the wash-out or ditch 33 causing a major bump to the vehicle 30 and the suspension components. When the wheel 31 reaches the far side of the wash-out or ditch 33, a second bump is caused as the front wheels 31 impact the side wall of the formation. These impacts can cause major stresses to the vehicle during normal operation over uneven terrain, as well as a reduction in the operator's comfort and in the stability of the spray boom (not shown).
Another conventional self-propelled vehicle 40 uses an endless track support assembly 41, as shown in FIG. 3. The conventional endless track vehicle 40 suffers from a "nose over" tendency when uneven terrain is traversed, such as mounds, levees, wash-outs or ditches. As shown in FIG. 3, this "nose over" tendency can cause a teeter totter effect when, for example, the front end 42 of the vehicle 40 drops into a wash-out or ditch 43. In some cases, this teeter totter effect can cause a portion 44 of the track assembly 41 to lose contact with the field surface, thereby reducing the operator's comfort as well as the stability of the spray boom (not shown). The single track assembly 41 also tends to destroy a substantial amount of standing crops during normal turns in the field.
Another known self-propelled vehicle for traversing uneven terrain is described in German Patent Publication No. 1,952,821. This vehicle includes a two-wheel assembly located at each of the four corners of the vehicle. Each two-wheel assembly comprises two successive wheels rotatably mounted on respective ends of a balancing lever arranged between the wheels. A suspension-like servo arrangement is connected to the balancing lever arrangement between the wheels so that the front wheels can be forced off the ground during normal operation to assume an elevated position. The wheel assemblies are arranged to provide equal weight distribution on both wheels of the assembly. The front wheel of each wheel assembly is substantially smaller than a rear wheel of each wheel assembly. In one embodiment, an endless chain is provided about each of the wheel assemblies to improve traction.
The vehicle described in the German '821 publication suffers from a number of disadvantages. The vehicle is not suitably equipped to traverse steep levees and deep wash-outs without damaging the vehicle or the ground surface, and without sacrificing the operator's comfort. For example, because there is no structure for limiting the pivotal movement of the balancing lever for each wheel assembly, the front wheel will, under some circumstances, tend to drop too far into a wash-out or trough following a levee, thereby causing damage to the vehicle or a substantial jolt to the operator. In addition, the equal weight distribution between the front and rear wheels increases the damage caused to levees, terraces, and other desired field terrain, as well as to standing crops.